Photographic flashlight apparatus with improved automatic light termination means

ABSTRACT

A photographic flashlight apparatus including a flash capacitor connected across a dc source; a flash tube and a thyristor series-connected across the flash capacitor so as to be made simultaneously conductive through the shutter operation of a photographic camera, whereby the flash tube initiates a light emission by discharging the voltage stored on the flash capacitor; and an automatic light termination circuit which includes a quench element made conductive in a predetermined length of time after the light emission is started by the flash tube and a flash termination capacitor stored with the dc source voltage and coupled between the thyristor and the quench element so as to terminate the light emission automatically upon conduction of the quench element by discharging the stored voltage across the flash termination capacitor through the conducting quench element, flash capacitor and flash tube and by turning off the thyristor forcefully. An over-flash current shunting circuit is provided in substantially parallel with the flash tube so as to cause at least part of an over-flash current to bypass which might otherwise flow into the flash tube at the instance of the light termination.

United States Patent Sato [ Apr. 15, 1975 Primary Examiner-James W.Lawrence Assistant Examiner-E. R. LaRoche Attorney, Agent, or FirmFlynn& Frishauf [75] Inventor: Fukuji Sato, Tokyo, Japan [5 ABSTRACT [73]Ass1gnee. Sato Kokl Co., Ltd., Toky Japan A h tographic flashlightapparatus including a flash [22] Filed: Dec. 17, 1973 capacitorconnected across a dc source; a flash tube and a thyristorseries-connected across the flash ca- [21] Appl' 425098 pacitor so as tobe made simultaneously conductive Related US. Application Data throughthe shutter operation of a photographic cam- [63] Continuationin-part ofSer. No. 259,475, June S, cm, whereby the flash tube initiates a lightemission y i972, abandoned, discharging the voltage stored on the flashcapacitor;

and an automatic light termination circuit which in- [30] Foreign Alicatio Priority D t cludes a quench element made conductive in a prede-Nov. 17 1971 Japan 46-92104 termihed length of after the light emissimis Dec. 14 1971 Japan 46-l0l258 Started by the flash tube and a flashtermination pacitor stored with the dc source voltage and coupled [52] sCL 315/241 P; 315/135; 3515/15. between the thyristor and the quenchelement so as to 315/159. 5/346 terminate the light emissionautomatically upon con- 51 Int. Cl. 1165b 41/32 ductiO" of the quenchelement by discharging the 5 Field f Search 315/149 151 159 241 R,stored voltage across the flash termination capacitor 315/241 P 135 340through the conducting quench element, flash capacitor and flash tubeand by turning off the thyristor [56] References Cited forcefully- UNlTES T PATENTS An over-flash current shunting circuit is provided in v 3705 330 12/1972 Rosenber 315,149 substantially parallel with the flashtube so as to cause 3 716 753 2 1973 Exner...... 315 241 P at least1hart of Over-flash current to bypass which 3:740:6lO 6/]973 Roncke 315241 P might Otherwise flow into the flash tube at the 3,787,704 1/1974Dennewitz et al 315/241 P ns ance of the light termination. 3,809,9515/1974 Vital et al. t 3l5/l49 Y 3,818,266 6/1974 Vital et al. 315 151 22l 9 Draw; F'gures 1 T l l l H r 1 DC 1 POWER SOURCE I l 34 I g TIMERCIRCUIT l saaaman s FIG. 55

FIG. 5A

POWER SOURCE TIMER CIRCUIT DC POWER SOURCE PI-IOTOGRAPHIC FLASHLIGIITAPPARATUS WITI-I IMPROVED AUTOMATIC LIGHT TERMINATION MEANSCROSS-REFERENCE TO RELATED APPLICATION This is continuation-in-part ofthe US. Pat. Application Ser. No. 259,475. filed on June 5, 1972. nowabandoned.

BACKGROUND OF THE INVENTION This invention relates to an electronic orphotographic flashlight apparatus for use with a photographic camera,and more particularly to the improvement of its automatic lighttermination means.

In the field of photographic flashlight apparatus, there has beenpreferably accepted the type which is provided with an automatic lighttermination means capable of automatically terminating the emission oflight by a flash tube in a predetermined length of time after saidemission is started in synchronism with the shutter operation of theassociated camera.

The prior art typical photographic flashlight apparatus of such typecomprises a flash capacitor connected across a dc source; a flash tubeand a thyristor connected in series across the flash capacitor so as tobe made simultaneously conductive through the shutter operation of aphotographic camera. whereby the flash tube initiates a light emissionby discharging the voltage stored on the flash capacitor; and anautomatic light termination means including a quench element madeconductive in a predetermined length of time after the light emission isstarted by the flash tube and a flash ter-' mination capacitor which isstored with the dc source voltage and disposed between the thyristor andquench element so as to terminate the light emission automatically uponconduction of the quench element by discharging the voltage storedacross the flash termination capacitor through the conducting quenchelement, flash capacitor and flash tube and by making the thyristorforcedly nonconducting.

However, the flashlight apparatus constructed as mentioned above has thedrawback that not only an exposure error is likely to occur but also aflash tube of considerably high withstanding voltage and large currentcapacity must be used, since an excess voltage about twiceof that of thedc source voltage derived from voltage across the flash terminationcapacitor added to voltage across the flash capacitor is applied to theflash tube at the moment of the flash termination or interruption,resulting in an over-current flow.

Accordingly, the main object of this invention is to provide aphotographic flashlight apparatus with improved light termination meansin which an optimum exposure is always attained so as to prevent anovercurrent flowing into the flash tube at the instance of the flashtermination.

SUMMARY OF THE INVENTION A photographic flashlight apparatus accordingto this invention is characterized in that an exposure control means forcausing at least part of an over-flash current to be shunted which mightotherwise flow into the flash tube at the moment of the flashtermination is provided substantially parallel with the flash tube.

The flashlight apparatus thus constructed has the advantage of not onlyalways effecting an optimum exposure but also admitting of applicationof a flash tube having lower withstanding voltage and current capacitythan in the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a schematic circuitdiagram ofa photographic flashlight apparatus embodying this invention;

FIG. 2 is a graph illustrating the relation of flash current and theduration of its introduction as observed with a flash tube used in aprior art flashlight apparatus;

FIG. 3 is a graph showing the relation of flash current and the durationof its introduction as observed with a flash tube used in a flashlightapparatus in accordance with this invention;

FIG. 4 shows a schematic circuit diagram ofa photographic flashlightapparatus according to another embodiment of this invention;

FIGS. 5A and 5B show different practical circuit arrangements of thetimer circuit shown in FIGS. 1 and FIG. 6 shows a schematic circuitdiagram modified from FIG. 1;

FIG. 7 shows a schematic circuit diagram modified from FIG. 4: and

FIG. 8 shows a schematic circuit diagram ofa photographic flashlightapparatus according to still another embodiment of this invention.

PREFERRED EMBODIMENTS OF THE INVENTION Referring now to FIG. 1, astorage or flash capacitor 12 is connected across the positive andnegative poles of a dc power source 11 having a relatively high voltage,for example, 300 volts. Connected across both the plates of the flashcapacitor 12 is a flashlight source 16 which includes a flash tube 14having one main electrode 1311 connected to one plate of the flashcapacitor 12 or the positive pole of the dc source 11 and a thyristor 15having the anode electrode connected to the other main electrode 131) ofthe flash tube 14 and the cathode electrode connected to the other plateof the flash capacitor 12 or the negative pole of the dc source 11. Theflash tube 14 has the ignition or trigger electrode 18 connected to oneend of the secondary winding 178 of an ignition or trigger transformer17 which comprises the primary and secondary windingselectromagnetically coupled to each other. The primary winding 17P ofthe transformer 17 has one end connected to the positive pole of the dcsource 11 via a capacitor 19 and a resistor 20. The other end of theprimary winding 17? is connected to the grounded negative pole of the dcsource 11 via a variable resistor 21 with the slidable arm 22 connectedto the gate electrode of the thyristor 15. A capacitor 24 is connectedbetween the junction 23 of the capacitor 19 with the resistor 20 and theground. Connected between the junction 23 and the junction 25 of theprimary winding 17? with the variable resistor 21 is a normally openswitch 26 which is closed in interlocking relationship with the shutteroperation of an associated photographic camera (not shown).

Also, an automatic flashlight termination means 27 is provided acrossboth the poles of the dc source 11 which comprises a resistor 2% havingone end connected to the positive pole of the dc source 11; a quenchelement, for example, a thyristor 29 whose main current cunduction pathis connected between the other end of the resistor 28 and the groundednegative pole of the dc source 11; a flash termination capacitor 32having one plate connected to the junction 30 of the resistor 28 and thethyristor 29 and the other plate connected to the junction 31 of theflash tube 14 and the thyristor 15; a resistor 33 connected between theother plate of the flash termination capacitor 32- and the ground; and atimer circuit 34 coupled with the gate electrode of the thyristor 29 soas to cause the thyristor 29 to be turned on in a predetermined lengthof time (generally us to 5 ms) after the emission of light is initiatedby the flash tube 14 included in the flashlight source 16 so as to behereinafter described. The elements or arrangements described above arepart of a conventional photographic flashlight apparatus.

The operation of such flashlight apparatus will now be described.

Firstly. let it be assumed that the switch 26 is kept open andpredetermined voltages in accordance with that of the dc source 11 areprecharged on the capacitors 12, 19, 24 and 32 with the indicatedpolarity.

When. under this condition. the shutter of the camera is manipulated.the switch 26 is closed in synchronism with the operation of theshutter. Consequently voltage stored on the capacitor 19 is dischargedthrough the closed switch 26 and the primary winding 17P of thetransformer 17 so that the transformer 17 is excited and the flash tube14 is triggered through the secondary winding 178 of the excitedtransformer 17. At the same time. voltage stored on the capacitor 24 isdischarged through the now closed switch 26 and the variable resistor21, causing the thyristor to be triggered. As a result. voltage storedon the flash capacitor 12 is discharged through the tired flash tube 14and thyristor 15 included in the flashlight source 16 and the flash tube14 initiates to produce light toward a fore ground subject (not shown)being photographed.

In the predetermined length of time after the emission of light isstarted by the flash tube 14, the thyristor 29 is triggered by the timercircuit 34. Accordingly, voltage stored on the flash terminationcapacitor 32 is discharged through the triggered thyristor 29, the flashcapacitor 12 and the conducting flash tube 14. At the same time. thedischarging voltage impressed across both poles of the flash terminationcapacitor 32 functions as a backward bias source to the thyristor 15,causing the thyristor 15 to be forcedly made nonconductive.

Therefore. the flash tube 14 acts to initiate the light emission whenthe switch 26 is closed and terminate said emission when the thyristor15 is rendered nonconductive by the discharge of the voltage storedacross the flash termination capacitor 32.

When, however. constructed only as mentioned above. a flashlightapparatus had the drawback that not only an exposure error was likely tooccur but also a flash tube of considerably high withstanding voltageand large current capacity must be used, since an excess amount ofvoltage about twice of that of the dc source voltage resulting fromvoltage across the flash termination capacitor 32 added to voltageacross the flash capacitor 12 was applied to the flash tube at theinstance ts of the flash termination, giving rise to an over-flashcurrent flow as shown in FIG. 2.

According to this invention, an over-flash current shunting means orexposure correction means 35 designed as hereinunder described isprovided substantially parallel with the flash tube.

The exposure correction means 35 comprises a diode 36 provided. ifrequired. and having the anode connected to the positive pole of the dcsource 11; a parallel circuit 39 consisting of a bypass capacitor 37 anda resistor 38 and connected at one end to the cathode of the diode 36;and a switch element, for example, a thyristor 40 whose anodecathodepath is connected between the other end of the parallel circuit 39 andthe ground. The thyristor 40 has its gate electrode coupled to the timercircuit 34 as in the case of the aforesaid thyristor 29.

The exposure correction means 35 thus arranged acts to cause at leastpart of the aforesaid over-flash current observed in the prior art whichmight otherwise flow into the flash tube 14 at the moment ts of theflash termination to be charged into, and shunted by. the capacitor 37,since the thyristor 40 is turned on simultaneously with the thyristor 29and the diode 36 is forwardly biased, thereby to prevent, as shown inFIG. 3, the over-flash current from flowing into the flash tube 14.Voltage stored across the capacitor 37 is discharged through theresistor 38 when the thyristor 40 is turned off by the timer circuit 34in the later described manner so as to render the capacitor 37 ready forthe next operation. Therefore. the photographic flashlight apparatusaccording to this invention can always attain an optimum exposure andalso admits of the use of a flash tube having a smaller withstandingvoltage and current capacity than in the prior art. Further theflashlight apparatus allows the use of a flash termination capacitorhaving a smaller capacitance than in the prior art. since a smallerflash current than in the prior art flows through the thyristor 29 uponthe light termination. The diode 36 acts to prevent the over-flashcurrent bypassed once by the capacitor 37 from running back to the flashtube 14.

According to this invention. a parallel circuit 43 consisting of aninduction coil 41 and a diode 42 of the indicated porality is furtherprovided between a positive source line 44 including the flash capacitor12 and a positive source line 45 to which the other circuit portions areconnected.

The induction coil 41 is intended to improve the differentiation di/dtof starting transient current i which flows from the flash capacitor 12and the flash termination capacitor 32 to the flash tube 14 and/or theexposure correction means 35 as well as the absorption of the over-flashcurrent during the starting transient pe-.

riod which flows from the flash capacitor 12 and the flash terminationcapacitor 32 to the exposure correction means 35. The diode 42 isadapted to prevent the current which flows once from the flash capacitor12 and the flash termination capacitor 32 to the flash tube 14 and/orthe exposure correction means 35 from flowing back to the capacitors 12and 32.

FIG. 4 shows a schematic circuit diagram of a photographic flashlightapparatus accordingto another embodiment of this invention. Theembodiment is different from that of FIG. 1 in that an exposurecorrection means 35 l is constituted by only a single bypass capacitor51 connected parallel with the resistor 28.

The operation of the exposure correction means 351 is essentially thesame as the exposure correction means 35 used in the embodiment of FIG.1 excepting that the thyristor 29 concurrently serves as the thyristor40, the resistor 28 concurrently serves as the resistor 38 and thethyristor 29 can be turned off more easier than in the embodiment ofFIG. 1 since voltage stored across the bypass capacitor 51 is dischargedthrough the resistor 28 immediately after the thyristor 29 is turnedoff. A diode 52 of the indicated polarity is provided between the flashtube 14 and the bypass capacitor 51 to attain the same effect as thediode 36 used in the embodiment of FIG. 1.

FIG. 5A shows a practical circuit arrangement of the timer circuit 34shown in FIGS. 1 and 4.

The timer circuit 341 comprises a photoelectric conversion element. forexample. an npn type phototransistor 63 whose collector is connected tothe positive pole of a dc source 61 via a normally open switch 62 closedin interlocking relationship with the shutter operation of theassociated camera together with the switch 26 and which is disposed toreceive light emitted by the flash tube 14 and reflected from thesubject so as to be rendered conductive; an integration capacitor 64connected between the emitter of the phototransistor 63 and the groundednegative pole of the dc source 61; and an amplifier 67 including an npntype emitter follower transistor 65 whose base is connected to theemitter of the phototransistor 63 and whose collector is connected tothe positive pole of the dc source 61 via the switch 62, and a resistor66 connected between the emitter of the transistor 65 and the ground.the base of the transistor 65 being connected to the gate electrode ofthe thyristor 29 (and that of the thyristor provided only in FIG. 1).

The operation of the timer circuit 341 will now be described.

When the switch 62 is closed in synchronism with the shutter operationof the camera and light reflected from the subject arrives, thephototransistor 63 is made conductive to produce photocurrent. Thephotocurrent thus obtained is charged on the capacitor 64 and integratedthereby in proportion to the total amount of light received by thephototransistor 63 with time.

When the integration voltage on the capacitor 64 reaches a predeterminedvalue, the transistor 65 is rendered conductive to cause the thyristor29 (and the thyristor 40) to be fired. Light reflected from the subjectdisappears and the switch 62 together with the switch 26 isagain openedimmediately after the completion of the camera shutter operation.

Accordingly, the phototransistor 63 is rendered nonconductive andvoltage stored on the capacitor 64 is discharged through the conductingtransistor 65 and the resistor 66 so as to make the capacitor 64 readyfor the next operation. The transistor 65 is made nonconductive when thevoltage charged across the capacitor 64 is reduced to about zero so asto be ready for the next operation. As a result. no trigger voltage isapplied to the thyristor 29 (and the thyristor 40). Therefore, thethyristor 29 (and the thyristor 40) is again turned off when the maincurrent flowing through the anodecathode path thereof falls below apredetermined value.

FIG. 5B shows another practical circuit arrangement of the timer circuit34.

The timer circuit 342 is constructed of a relaxation oscillator 80 whichcomprises a series circuit 75 consisting of a resistor 73 and acapacitor 74 and connected across both poles of a dc source 71 via anormally open switch 72 closed interlockingly with the shutter operationof the associated camera together with the switch 26; an npn typeunijunction transistor or double base diode 79 whose emitter isconnected to the junction 76 of the resistor 73 and the capacitor 74,whose first base is connected to the grounded negative pole of the dcsource 71 via a resistor 77 and whose second base is connected to thenongrounded side of the series circuit via a variable resistor 78, thefirst base of the double base diode 79 being connected to the gateelectrode of the thyristor 29 (and thyristor 40).

The operation of the timer circuit 342 will now be described.

When the switch 72 is closed in synchronism with the shutter operationof the camera. the capacitor 74 is charged with a proper level ofvoltage to cause the double base diode 79 to be triggered after a lengthof time determined by the time constant arrived at by multiplying theresistance of the resistor 73 by the capacitance of the capacitor 74.

As a result. the double base diode 79 is brought to a conducting stateand the relaxation oscillator 80 generates an output signal so as tocause the thyristor 29 (and thyristor 40) to be triggered. The switch 72together with the switch 26 is again opened immediately after thecompletion of the camera shutter operation. Consequently, voltage storedacross the capacitor 74 is discharged through the conducting double basediode 79 and the resistor 77 so as to make the capacitor 74 ready forthe next operation.

The double base diode 79 is made nonconductive when the voltage chargedacross the capacitor 74 is reduced to about zero ready for the nextoperation.

Accordingly, the timer circuit 342 of FIG. 5B operates in essentiallythe same manner as the timer circuit 341 of FIG. 5A.

FIG. 6 shows a schematic circuit diagram of one modification of FIG. 1.

The modification is different from the embodiment of FIG. 1 in thatconventional quench or switch tubes 81 and 82 are used in place of thethyristors 29 and 40 employed in the embodiment of FIG. 1. The quenchtubes 81 and 82 have trigger electrodes coupled with the timer circuit34 via a common ignition transformer 83, a coupling capacitor 84 and aswitching thyristor 85. The thyristor 85 has an anodecathode pathconnected via a resistor 86 across the dc source 11 and a gate electrodecoupled with the timer circuit 34.

FIG. 7 shows a schematic circuit diagram of one modification of FIG. 4.

The modification is different from the embodiment of FIG. 4 in that aconventional quench tube 91 designed in the same manner as the quenchtube 81 is used in place of the thyristor 29 used in the embodiment ofFIG. 4.

It will be apparent to those skilled in the art that the modificationsof FIGS. 6 and 7 operate in essentially the same manner as theembodiments of FIGS. 1 and 4.

graphic flashlight apparatus according to still another embodiment ofthis invention.

The embodiment is different from the embodiment of FIG. 1 or 4 in thatan availability confirming means 130 constructed as hereinafterdescribed is further provided and a trigger circuit portion for theflash tube FIG. 8 shows a schematic circuit diagram of a photo- 14 andthe thyristor 15 is modified as hereinunder described.

The trigger circuit portion 100 includes a series circuit 103 consistingof a resistor 101 and a capacitor 102 and connected between the positivesource line 45 and the ground. Connected in series between the junction104 of the resistor 101 with the capacitor 102 and the ground are aresistor 105, the normally open switch 26 and a series connection 109 ofthree resistors 106. I07 and 108.

Connected between the junction 110 ofthe switch 26 and the seriesconnection 109 is a parallel circuit 113 consisting of a capacitor 111and a zener diode 112. The aforesaid junction 23 is connected to theanode of a thyristor 114. The thyristor 114 has a gate electrodeconnected to the junction 115 of the resistors 107 and 108 as well as toground via a capacitor 116 and a cathode connected to ground via aparallel circuit 119 consisting of a capacitor 117 and a resistor 118 aswell as to the other end of the primary winding 17P of the aforesaidtrigger transformer 17. Connected in series between the junction 120 ofthe parallel circuit 119 with the primary winding 17? and the ground area resistor 121 and a resistor 122. The junction 123 of the resistors 121and 122 is connected to the gate electrode of the thyristor 15.

The operation of the trigger circuit portion 100 will now be described.

Immediately before the shutter of the associated camera is manipulated.the switch 26 is kept open and the capacitors 12, 19, 24, 32 and 102 areprecharged with predetermined voltages in accordance with that of the dcsource 11. When under this condition. the switch 26 is closedinterlockingly with the camera shut ter operation. voltage stored on thecapacitor 102'is discharged through the resistor 105, the closed switch26 and the series connection 109 of three resistors 106 to 108 so as tocause a constant voltage smoothed by the capacitor 111, for example, tovolts to be induced across the zener diode 112. The constant voltagethus induced is divided by the three resistors 106 to 108. The thyristor114 is triggered by the divided voltage appearing across the resistor108. As a result, voltage stored on the capacitor 19 is dischargedthrough the fired thyristor 114 and the primary winding 17? of thetransformer 17 so as to cause the flash tube 14 to be triggered. At thesame time, voltage stored on the capacitor 24 is discharged through theconducting thyristor 114 and the resistor 118 as well as theseriesconnected resistors 121 and 122 connected parallel with theresistor 118 so as to cause the thyristor to be triggered. Therefore.the trigger circuit portion 100 of FIG. 8 functions in essentially thesame manner as that of FIG. 1 or 4.

A series connection of a resistor 124 and a capacitor 125 may beprovided in parallel with the switch 26 in order to shunt sparkdischarge voltage likely to occur when the switch 26 is closed.

The availability-confirming means 130 includes anavailability-confirming element such as an indicator lamp 135 whose oneelectrode is connected to the aforesaid junction of the flashtermination capacitor 32 with the resistor 28 via a resistor 131 andalso to the positive power source line 45 via a series connection 134 ofa diode 132 having the indicated polarity and a resistor 133. Theindicator lamp 135 has the other electrode connected to the ground via aresistor 136 and also to the junction 137 of the resistors 106 and 107via adiode 138 of the indicated polarity.

The operation of the availability-confirming means will now bedescribed.

A current conduction path 139 for lighting the indicator lamp is formedby the series route consisting of the resistor 28, resistor 131,indicator lamp 135 and resistor 136.

Thus. prior to the shutter operation of the camera the indicator lamp135 is designed to be turned on only when sufficient voltage to allowthe thyristor 15 to be turned off by the discharge thereof as mentionedabove is precharged across the flash termination capacitor 32 and alsosufficient voltage to permit the optimum emission of light by the flashtube 14 is precharged across the flash capacitor 12.

That is, in the case where the flash termination capacitor 32 isprecharged with the sufficient voltage to cause the thyristor 15 to beturned off by the discharge thereof but the flash capacitor 12 is onlyprecharged with insufficient voltage to permit the optimum emission oflight by the flash tube, then current corresponding to the voltagecharged on the capacitor 32 is shunted through the resistor 131, the nowforwardly biased diode 132 and the resistor 133 by substantially ceasingto flow into the indicator lamp 135 so asto turn off the indicator lamp135.

In the contrary case where the flash capacitor 12 is precharged with thesufficient voltage to allowthe optimum emission of light by the flashtube 14 but the flash termination capacitor 32 is only precharged withinsufficient voltage to cause the thyristor 15 to be turned off by thedischarge thereof, then part of current proportional to the voltagecharged on the capacitor 12 flows through the flash terminationcapacitor 32 so as to cause the capacitor 32 to be charged, thus stillpreventing the indicator lamp 135 from being turned on.

Even if, under the condition where either of the flash terminationcapacitor 32 and the flash capacitor 12 is precharged with the aforesaidsufficient voltage, the.

switch 26 is closed by the misoperation of the shutter of the camera,part of current corresponding to the voltage obtained by dividing theaforesaid constant voltage induced across the zener diode 112 by thethree-series connected resistors 106 to 108 is shunted through the nowforwardly biased diode 138 and the conflrmingmeans 130 has the advantagecapable of preventing the erroneous camera shutter operation.

In FIG. 8, reference numeral 343 is a timer circuit which is designed touse as a dc source 141 for the op eration thereof the aforesaid constantvoltage induced across the zener diode 112 upon the closure of theswitch 26 interlocking with the shutter operation of the camera.

The timer circuit 343 comprises an npn type phototransistor 144 whosecollector is connected to the dc source 141 via a capacitor 142 as wellas a resistor 143 and which is disposed to receive light reflected fromthe subject being photographed; and an amplifier 153 including a pnptype transistor 148 whose base is connected to the collector of thephototransistor 144, whose emitter is connected to the slidable arm 146of a variable resistor 145 having one end connected to the dc source 141and whose collector is connected to the mally open switch which isclosed interlockingly with the shutter operation of said camera: and adouble base diode whose emitter is connected to the junction of saidcapacitor with said first resistor. one of the bases of said double basediode being connected to one end of said series circuit via a secondresistor and coupled with said quench element. and the other. base ofsaid double base diode being connected to the other end of said seriescircuit via a third resistor.

9. Apparatus as claimed in claim 1 further including anavailability-confirming means which comprises an indicator lamp havingone electrode thereof connected to the junction of said flashtermination capacitor with said quench element as well as to the highpotential side of said dc source via a resistor and a diode. the diodebeing connected with a backward polarity relative to said dc source theother electrode of said'indicator lamp being connected to the lowpotential side of said dc source via another resistor. said indicatorlamp being turned on only when sufficient voltage to permit the emissionof light by said flash tube is precharged on said flash capacitor andalso sufficient discharging voltage to cause said quench element to beturned off is precharged on said flash termination capacitor.

10. Apparatus as claimed in claim 9, comprising a trigger source forsaid flashlight source, and wherein said availability-confirming meansfurther includes a further diode coupled between said trigger source andsaid other electrode of said indicator lamp and being operative to shuntpart of the current from said trigger source only upon an erroneousshutter operation of an associated camera under the condition whereinsufficient voltage to permit the optimum emission of light by saidflash tube is precharged on said flash capacitor so as to prevent saidflash tube from being triggered.

11. A photographic flashlight apparatus comprising: a flash capacitorconnected across a dc source of a predetermined voltage; v

a flashlight source connected across said flash capacitor and includinga flash tube and a thyristor which are simultaneously renderedconductive upon the shutter operation of a photographic camera so as toinitiate a light emission by said flash tube;

an automatic light termination means disposed across said flashcapacitor and including a quench element; a timer circuit coupled withsaid quench element so as to cause said quench element to be turned on apredetermined period of time after the emission of light is initiated bysaid flash tube; and a flash termination capacitor coupled with saidthyristor included in said flashlight source and said quench element andprecharged with voltage corresponding to that of said dc source foreffecting discharge upon the conduction of said quench element by saidtimer circuit through said conducting quench element, said flashcapacitor and said flashlight source so as to turn off said thyristor;

an exposure correction means including a resistor connected in parallelwith a bypass capacitor, said parallel circuit being coupledsubstantially in parallel with said flash tube and being operative toshunt at least part of an over-flash current which'might otherwise flowinto said flash tube upon the flash termination thereof; and

an availability-confirming means which comprises an indicator lamphaving one electrode thereof connected .to the junction of said flashtermination capacitor with said quench element as well as to the highpotential side of said dc source via a resistor and a diode. the diodebeing connected with a backward polarity relative to said dc source, theother electrode of said indicator lamp being connected to the lowpotential side of said dc source via another resistor, said indicatorlamp being turned on only when sufficient voltage to permit the emissionof light by said flash tube is precharged on said flash capacitor andalso sufficient discharging voltage to cause said quench element to beturned off is precharged on said flash termination capacitor.

12. Apparatus as claimed in claim 11, comprising a trigger source forsaid flashlight source, and wherein said availability-confirming meansfurther includes a further diode coupled between said trigger source andsaid other electrode of said indicator lamp and being operative to shuntpart of the current from said trigger source only upon an erroneousshutter operation of an associated camera under the condition whereinsufficient voltage to permit the optimum emission of light by saidflash tube is precharged on said flash capacitor so as to prevent saidflash tube from being triggered.

13. In a photographic flashlight apparatus comprisa flash capacitorconnected across a dc source of a predetermined voltage;

a flashlight source connected across said flash capacitor and includinga flash tube and a thyristor which are simultaneously renderedconductive upon the shutter operation of a photographic camera so as toinitiate a light emission by said flash tube; and

an automatic light termination meansdisposed across said flash capacitorand including a quench element; a timer circuit coupled with said quenchelement so as to cause said quench element to be turned on apredetermined period of time after the emission of light is initiated bysaid flash tube; and

a flash termination capacitor coupled with said thy-.

circuit which is coupled substantially in parallel.

with said flash tube between the high potential side of said dc sourceand the junction of said flash termination capacitor with said quenchelement, said parallel circuit including a resistor and a bypasscapacitor connected in parallel with said resistor, said parallelcircuit being operative to shunt at least part of an over-flash currentwhich might otherwise flow into said flash tube upon the flashtermination thereof.

14. Apparatus as claimed in claim 13, wherein said exposure correctionmeans further includes a diode connected between said parallel circuitand said flashlight source with a forward polarity with respect to saiddc source.

15. Apparatus as claimed in claim 13, wherein said timer circuitincluded in said automatic light termination means comprises aphotoelectric conversion eleground via a resistor l'47,,and an npn typetransistor 152 whose base is connected to the emitter of thephototransistor 144 as well as the collector of the transistor 148,whose collector is connected to the dc source 141 via a resistor 149 andwhose emitter is connected to the ground via a capacitor 150 as well asa resistor 151. the emitter of the transistor 152 being connected to thegate electrode of said thyristor 29 and the other end of said variableresistor 145 being connected to the ground via a resistor 153.

It will be apparent to those skilled in the art that the timer circuit343 constructed as mentioned above operates in essentially the samemanner as the timer circuit 341 shown in FIG. A.

By way of illustration. a typical circuit defining this invention isconstructed as shown in FIG. 8 and by selecting the value of mainelements used therein as follows:

ductive simultaneously with said quench element. and a parallel circuitwhich includes a resistor and a bypass capacitor coupled in parallelwith said resistor. said parallel circuit being operative to shuntthrough said conducting switch element at least part of an over-flashcurrent which might otherwise flow into said flash tube upon the flashtermination thereof.

2. Apparatus as claimed in claim 1. wherein said series arrangementfurther includes a diode connected in series with said switch elementand with a forward polarity with respect to said dc source.

3. Apparatus as claimed in claim 1. wherein said switch element as wellas said quench element comprises a thyristor.

4. Apparatus as claimed in claim 1. wherein said switch element as wellas said quench element comprises a quench tube.

Resistors Capacitors Induction coil 2.2 M!) I2 500 al- 41 I70 ;LH 28 5.IKO I9 0.047 .F 33 3.9 K!) 24 0.047 aF I0] I M!) 32 2.2 ,uF I05 I0 KO. 5I I0 F I06 I0 KS) l l I 0.047 [.LF I07 4.7 K!) I I6 0.05 ;LF 108 l K!) I17 0.15 uF I I8 I50 (1 I 0.047 [LF I2I 220 .(1 I42 0.068 .F I22 220 .0I50 0.05 ;:.F I24 I0 Kl I3 I 470 KO.

I47 I KI).

ISI 470 .(1

What is claimed is:

1. In a photographic flashlight apparatus comprising:

a flash capacitor connected across a dc source of a predeterminedvoltage;

a flashlight source connected across said flash capacitor and includinga flash tube and a thyristor which are simultaneously renderedconductive upon the shutter operation of a photographic camera so as toinitiate a light emission by'said flash tube; and

an automatic light termination means disposed across said flashcapacitor and including a quench element. a timer circuit coupled withsaid quench element so as to cause said quench element to be turned on apredetermined period of time after the emission of light is initiated bysaid flash tube, and a flash termination capacitor coupled with saidthyristor included in said flashlight source and said quench element andprecharged with voltage corresponding to that of said dc source foreffecting discharge upon the conduction of said quench element by saidtimer circuit through said conducting quench element, said flashcapacitor and said flashlight source so as to turn off said thyristor;

the improvement comprising:

an exposure correction means including a series arrangement which isconnected across said flash capacitor and which includes a switchelement coupled with said timer circuit so as to be made con- 5.Apparatus as claimed in claim I further including an inductor connectedbetween a power source line for said flash capacitor and a power sourceline for the remaining elements.

6. Apparatus as claimed in claim 1 further including a diode connectedin parallel with said inductor with a backward polarity relative to saiddc source.

7. Apparatus as claimed in claim 1. wherein said timer circuit includedin said automatic light termination means comprises a photoelectricconversion element which is connected to a dc source via a normally openswitch which is closed interlockingly with the shutter operation of saidcamera. and which is disposed to receive light emitted by said flashtube and reflected from a foreground subject so as to producephotocurren't proportional to the received amount of light; and anintegration capacitor coupled with said photoelectric conversion elementand said quench element for integrating with time the photocurrentflowing through said photoelectric conversion element, said quenchelement being turned on responsive to the integrated voltage.

8. Apparatus as claimed in claim 1, wherein said timer circuit includedin said automatic light termination means comprises a relaxationoscillator which includes a series circuit having a first resistor and acapacitor connected in series with said first resistor, said seriescircuit being connected to'a dc source via a norment which is connectedto a dc source via a normally open switch which is closed interlockinglywith the shutter operation of said camera. and which is disposed toreceive light emitted by said flash tube and reflected from a foregroundsubject so as to produce photocurrent proportional to the receivedamount of light: and an integration capacitor coupled with saidphotoelectric conversion element and said quench element for integratingwith time the photocurrent flowing through said photoelectric conversionelement. said quench element being turned on responsive to theintegrated voltage.

16. Apparatus as claimed in claim 13. wherein said timer circuitincluded in said automatic light termination means comprises arelaxation oscillator which includes a series circuit having a firstresistor and a capacitor connected in series with said first resistor,said series circuit being connected to a dc source via a normally openswitch which is closed interlockingly with the shutter operation of saidcamera; and a double base diode whose emitter is connected to thejunction of said capacitor with said first resistor one of the bases ofsaid double base diode being connected to one end of said series circuitvia a second resistor and coupled with said quench element. and theother base of said double base diode being connected to the other end ofsaid series circuit via a third resistor.

17. Apparatus as claimed in claim 13 wherein said quench elementcomprises a thyristor.

18. Apparatus as claimed in claim 13 wherein said quench elementcomprises a quench tube.

19. Apparatus as claimed in claim 13 further including an inductorconnected between a power source line for said flash capacitor and apower source line for the remaining elements.

20. Apparatus as claimed in claim 19 further including a diode connectedin parallel with said inductor with a backward polarity relative to saiddc source.

21. Apparatus as claimed in claim 13 further including anavailability-confirming means which comprises an indicator lamp havingone electrode thereof connected to the junction of said flashtermination capacitor with said quench element as well as to the highpotential side of said dc source via a resistor and a diode. the diodebeing connected with a backward polarity relative to said dc source. theotherelectrode of said indicator lamp being connected to the lowpotential side of said dc source via another resistor said indicatorlamp being turned on only when sufficient voltage to permit the emissionof light by said flash tube is precharged on said flash capacitor andalso sufficient discharging voltage to cause said quench element to beturned off is precharged on said flash termination capacitor.

22. Apparatus as claimed in claim 21. comprising a trigger source forsaid flashlight source, and wherein said availability-confirming meansfurther includes a further diode coupled between said trigger source andsaid other electrode of said indicator lamp and being operative to shuntpart of the current from said trigger source only upon an erroneousshutter operation of an associated camera under the condition whereinsufficient voltage to permit the optimum emission of light by saidflash tube is precharged on said flash capacitor so as to prevent saidflash tube from being triggered.

1. In a photographic flashlight apparatus comprising: a flash capacitorconnected across a dc source of a predetermined voltage; a flashlightsource connected across said flash capacitor and including a flash tubeand a thyristor which are simultaneously rendered conductive upon theshutter operation of a photographic camera so as to initiate a lightemission by said flash tube; and an automatic light termination meansdisposed across said flash capacitor and including a quench element, atimer circuit coupled with said quench element so as to cause saidquench element to be turned on a predetermined period of time after theemission of light is initiated by said flash tube, and a flashtermination capacitor coupled with said thyristor included in saidflashlight source and said quench element and precharged with voltagecorresponding to that of said dc source for effecting discharge upon theconduction of said quench element by said timer circuit through saidconducting quench element, said flash capacitor and said flashlightsource so as to turn off said thyristor; the improvement comprising: anexposure correction means including a series arrangement which isconnected across said flash capacitor and which includes a switchelement coupled with said timer circuit so as to be made conductivesimultaneously with said quench element, and a parallel circuit whichincludes a resistor and a bypass capacitor coupled in parallel with saidresistor, said parallel circuit being operative to shunt through saidconducting switch element at least part of an over-flash current whichmight otherwise flow into said flash tube upon the flash termiNationthereof.
 2. Apparatus as claimed in claim 1, wherein said seriesarrangement further includes a diode connected in series with saidswitch element and with a forward polarity with respect to said dcsource.
 3. Apparatus as claimed in claim 1, wherein said switch elementas well as said quench element comprises a thyristor.
 4. Apparatus asclaimed in claim 1, wherein said switch element as well as said quenchelement comprises a quench tube.
 5. Apparatus as claimed in claim 1further including an inductor connected between a power source line forsaid flash capacitor and a power source line for the remaining elements.6. Apparatus as claimed in claim 1 further including a diode connectedin parallel with said inductor with a backward polarity relative to saiddc source.
 7. Apparatus as claimed in claim 1, wherein said timercircuit included in said automatic light termination means comprises aphotoelectric conversion element which is connected to a dc source via anormally open switch which is closed interlockingly with the shutteroperation of said camera, and which is disposed to receive light emittedby said flash tube and reflected from a foreground subject so as toproduce photocurrent proportional to the received amount of light; andan integration capacitor coupled with said photoelectric conversionelement and said quench element for integrating with time thephotocurrent flowing through said photoelectric conversion element, saidquench element being turned on responsive to the integrated voltage. 8.Apparatus as claimed in claim 1, wherein said timer circuit included insaid automatic light termination means comprises a relaxation oscillatorwhich includes a series circuit having a first resistor and a capacitorconnected in series with said first resistor, said series circuit beingconnected to a dc source via a normally open switch which is closedinterlockingly with the shutter operation of said camera; and a doublebase diode whose emitter is connected to the junction of said capacitorwith said first resistor, one of the bases of said double base diodebeing connected to one end of said series circuit via a second resistorand coupled with said quench element, and the other base of said doublebase diode being connected to the other end of said series circuit via athird resistor.
 9. Apparatus as claimed in claim 1 further including anavailability-confirming means which comprises an indicator lamp havingone electrode thereof connected to the junction of said flashtermination capacitor with said quench element as well as to the highpotential side of said dc source via a resistor and a diode, the diodebeing connected with a backward polarity relative to said dc source, theother electrode of said indicator lamp being connected to the lowpotential side of said dc source via another resistor, said indicatorlamp being turned on only when sufficient voltage to permit the emissionof light by said flash tube is precharged on said flash capacitor andalso sufficient discharging voltage to cause said quench element to beturned off is precharged on said flash termination capacitor. 10.Apparatus as claimed in claim 9, comprising a trigger source for saidflashlight source, and wherein said availability-confirming meansfurther includes a further diode coupled between said trigger source andsaid other electrode of said indicator lamp and being operative to shuntpart of the current from said trigger source only upon an erroneousshutter operation of an associated camera under the condition whereinsufficient voltage to permit the optimum emission of light by saidflash tube is precharged on said flash capacitor so as to prevent saidflash tube from being triggered.
 11. A photographic flashlight apparatuscomprising: a flash capacitor connected across a dc source of apredetermined voltage; a flashlight source connected across said flashcapacitor and including a flash tube and a thyristor which aresimultaneoUsly rendered conductive upon the shutter operation of aphotographic camera so as to initiate a light emission by said flashtube; an automatic light termination means disposed across said flashcapacitor and including a quench element; a timer circuit coupled withsaid quench element so as to cause said quench element to be turned on apredetermined period of time after the emission of light is initiated bysaid flash tube; and a flash termination capacitor coupled with saidthyristor included in said flashlight source and said quench element andprecharged with voltage corresponding to that of said dc source foreffecting discharge upon the conduction of said quench element by saidtimer circuit through said conducting quench element, said flashcapacitor and said flashlight source so as to turn off said thyristor;an exposure correction means including a resistor connected in parallelwith a bypass capacitor, said parallel circuit being coupledsubstantially in parallel with said flash tube and being operative toshunt at least part of an over-flash current which might otherwise flowinto said flash tube upon the flash termination thereof; and anavailability-confirming means which comprises an indicator lamp havingone electrode thereof connected to the junction of said flashtermination capacitor with said quench element as well as to the highpotential side of said dc source via a resistor and a diode, the diodebeing connected with a backward polarity relative to said dc source, theother electrode of said indicator lamp being connected to the lowpotential side of said dc source via another resistor, said indicatorlamp being turned on only when sufficient voltage to permit the emissionof light by said flash tube is precharged on said flash capacitor andalso sufficient discharging voltage to cause said quench element to beturned off is precharged on said flash termination capacitor. 12.Apparatus as claimed in claim 11, comprising a trigger source for saidflashlight source, and wherein said availability-confirming meansfurther includes a further diode coupled between said trigger source andsaid other electrode of said indicator lamp and being operative to shuntpart of the current from said trigger source only upon an erroneousshutter operation of an associated camera under the condition whereinsufficient voltage to permit the optimum emission of light by saidflash tube is precharged on said flash capacitor so as to prevent saidflash tube from being triggered.
 13. In a photographic flashlightapparatus comprising: a flash capacitor connected across a dc source ofa predetermined voltage; a flashlight source connected across said flashcapacitor and including a flash tube and a thyristor which aresimultaneously rendered conductive upon the shutter operation of aphotographic camera so as to initiate a light emission by said flashtube; and an automatic light termination means disposed across saidflash capacitor and including a quench element; a timer circuit coupledwith said quench element so as to cause said quench element to be turnedon a predetermined period of time after the emission of light isinitiated by said flash tube; and a flash termination capacitor coupledwith said thyristor included in said flashlight source and said quenchelement and precharged with voltage corresponding to that of said dcsource for effecting discharge upon the conduction of said quenchelement by said timer circuit through said conducting quench element,said flash capacitor and said flashlight source so as to turn off saidthyristor; the improvement comprising: an exposure correction meansincluding a parallel circuit which is coupled substantially in parallelwith said flash tube between the high potential side of said dc sourceand the junction of said flash termination capacitor with said quenchelement, said parallel circuit including a resistor and a bypasscapacitor connected in parallel with said resistor, Said parallelcircuit being operative to shunt at least part of an over-flash currentwhich might otherwise flow into said flash tube upon the flashtermination thereof.
 14. Apparatus as claimed in claim 13, wherein saidexposure correction means further includes a diode connected betweensaid parallel circuit and said flashlight source with a forward polaritywith respect to said dc source.
 15. Apparatus as claimed in claim 13,wherein said timer circuit included in said automatic light terminationmeans comprises a photoelectric conversion element which is connected toa dc source via a normally open switch which is closed interlockinglywith the shutter operation of said camera, and which is disposed toreceive light emitted by said flash tube and reflected from a foregroundsubject so as to produce photocurrent proportional to the receivedamount of light; and an integration capacitor coupled with saidphotoelectric conversion element and said quench element for integratingwith time the photocurrent flowing through said photoelectric conversionelement, said quench element being turned on responsive to theintegrated voltage.
 16. Apparatus as claimed in claim 13, wherein saidtimer circuit included in said automatic light termination meanscomprises a relaxation oscillator which includes a series circuit havinga first resistor and a capacitor connected in series with said firstresistor, said series circuit being connected to a dc source via anormally open switch which is closed interlockingly with the shutteroperation of said camera; and a double base diode whose emitter isconnected to the junction of said capacitor with said first resistor,one of the bases of said double base diode being connected to one end ofsaid series circuit via a second resistor and coupled with said quenchelement, and the other base of said double base diode being connected tothe other end of said series circuit via a third resistor.
 17. Apparatusas claimed in claim 13 wherein said quench element comprises athyristor.
 18. Apparatus as claimed in claim 13 wherein said quenchelement comprises a quench tube.
 19. Apparatus as claimed in claim 13further including an inductor connected between a power source line forsaid flash capacitor and a power source line for the remaining elements.20. Apparatus as claimed in claim 19 further including a diode connectedin parallel with said inductor with a backward polarity relative to saiddc source.
 21. Apparatus as claimed in claim 13 further including anavailability-confirming means which comprises an indicator lamp havingone electrode thereof connected to the junction of said flashtermination capacitor with said quench element as well as to the highpotential side of said dc source via a resistor and a diode, the diodebeing connected with a backward polarity relative to said dc source, theother electrode of said indicator lamp being connected to the lowpotential side of said dc source via another resistor, said indicatorlamp being turned on only when sufficient voltage to permit the emissionof light by said flash tube is precharged on said flash capacitor andalso sufficient discharging voltage to cause said quench element to beturned off is precharged on said flash termination capacitor. 22.Apparatus as claimed in claim 21, comprising a trigger source for saidflashlight source, and wherein said availability-confirming meansfurther includes a further diode coupled between said trigger source andsaid other electrode of said indicator lamp and being operative to shuntpart of the current from said trigger source only upon an erroneousshutter operation of an associated camera under the condition whereinsufficient voltage to permit the optimum emission of light by saidflash tube is precharged on said flash capacitor so as to prevent saidflash tube from being triggered.